Kennedy, L. A. | bioRxiv Science

bioRxiv2026

Understanding the impact of sodium sulfide on the invasive growth of wine yeast

Yeasts ability to invade surfaces has important implications for infections and food contamination. Invasive growth in yeast is influenced by genetic and environmental factors. In this exploratory study, we used a systematic experimental design to identify conditions under which sulfide-induced invasive growth can be reliably observed and quantified and investigated the effects of sulfide, gene deletions, and environmental conditions on the invasive behaviour of the wine yeast strain AWRI 796. Sulfide enhanced invasion in the (parent) AWRI 796 strain under nitrogen-limiting conditions, although its effect was obscured by experimental variability and pre-culture conditions. Genetic factors had a major effect on the overall invasive phenotype, with deletion of key genes suppressing invasion. Most gene-deletion mutants did not significantly affect how the colony responded to sulfide. In addition to sulfide and genotype, environmental conditions also influenced invasive behaviour. The pre-2xSLAD pre-culture condition was best for detecting sulfide-induced growth, and later plate washing time and decreased nutrient levels enhanced invasiveness. Our experimental design and findings provide a framework for understanding the determinants of yeast invasiveness, which may inform future studies on filamentous yeast behaviour.

microbiology↗

bioRxiv2020

The Histoplasma capsulatum DDR48 Gene Is Required For Survival Within Macrophages, Response To Oxidative Stress, And Resistance to Antifungal Drugs

Histoplasma capsulatum (Hc) is a systemic, dimorphic fungal pathogen that affects upwards of 500,000 individuals in the United States annually. Hc grows as a multicellular mold at environmental temperatures; whereas, upon inhalation into a human or other mammalian host, it transforms into a unicellular, pathogenic yeast. This manuscript is focused on characterizing the DNA damage-responsive gene HcDDR48. HcDDR48 was originally isolated via a subtractive DNA library enriched for transcripts enriched in the mold-phase of Hc growth. Upon further analysis we found that HcDDR48 is not just expressed in the mold morphotype, but both growth programs dependent upon the environment. We found that HcDDR48 is involved in oxidative stress response, antifungal drug resistance, and survival within resting and activated macrophages. Growth of ddr48{Delta} yeasts was severely decreased when exposed to the reactive oxygen species generator paraquat, as compared to wildtype controls. We also found that ddr48{Delta} yeasts were 2-times more sensitive to the antifungal drugs amphotericin b and ketoconazole. To test HcDDR48s involvement in vivo, we infected resting and activated RAW 264.7 murine macrophages with Hc yeasts and measured yeast survival 24-hours post-infection. We observed a significant decrease in yeast recovery in the ddr48{Delta} strain compared to wildtype Hc levels. Herein, we demonstrate the importance of maintaining a functional copy of HcDDR48 in order for Hc yeasts to sense and respond to numerous environmental and host-associated stressors. ImportanceHistoplasma capsulatum is an intracellular pathogen of phagocytes, where it subverts immune recognition and avoids killing by the innate immune system. Macrophages provide a permissive environment for Hc replication and killing only occurs upon the onset of the T-cell driven adaptive immune response. Hc has evolved numerous virulence factors that aid in its survival against host-derived ROS and RNS in vivo. While these virulence factors have been described in past years, only a few reports describing the regulation of these genes and how this intricate system leads to fungal survival. In this study, we characterized the stress response gene DDR48 and determined it to be indispensable for Hc survival within macrophages. HcDDR48 regulates transcript levels of superoxide dismutases and catalases responsible for detoxification of ROS and contributes to antifungal drug resistance. Our studies highlight DDR48 as a potential target to control Hc infection and decrease the severity of the disease process.

microbiology↗